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My period is very light, am I pregnant?

One of the first signs of pregnancy can be a light period, and it can be difficult to tell whether it is due to pregnancy or not as the bleed can occur at around the same time of a ‘normal’ period. Light bleeding that occurs early on in pregnancy can be due to implantation bleeding, which is where the fertilised egg buries itself into the womb. As it does so, part of the womb wall sheds and it is this that causes the bleeding, which is harmless and normal.

How to distinguish implantation bleeding

Implantation bleeding differs from a normal period in that it is a smaller amount of blood loss than a normal period. It may be just some spotting, and should not be enough to fill several tampons. The colour is often dark brown or light pink rather than the bright red blood of a normal period, and there are no clots. The bleeding shouldn’t last a long time, perhaps only a few hours, although it could be up to a week.

If your periods are regular, implantation bleeding happens a few days earlier than when a normal period is due, so it is often mistaken for an early period. There may be a slight abdominal cramp that occurs when the egg attaches onto the womb, but this cramping is generally faint and does not increase in strength over time. If you have severe pain associated with the light bleed, then it is unlikely that it’s due to implantation bleeding. Other signs of early pregnancy can occur with implantation bleeds, which include mood swings, breast tenderness and oily skin.

Other causes of bleeding in early pregnancy

Light bleeding in early pregnancy is relatively common, and while implantation bleeding is the most common cause, there are other causes. In pregnancy, the hormonal changes can cause the cervix to become thinner and more vascular. This may cause it to bleed more easily on trauma, such as just after penetrative sex, for example. This type of bleeding is very light, lasts less than a day, is harmless, and has no other associated symptoms.

Heavier bleeding during the first 12 weeks of pregnancy can be due to miscarriage, which is very common in early pregnancy compared with later on in pregnancy, and is normally not something that could have been prevented. Unfortunately, it can happen when there is a genetic or developmental abnormality in the growing foetus, or a hormonal or blood clotting problem.

In pregnancy, the hormonal changes can cause the cervix to become thinner and more vascular. This may cause it to bleed more easily on trauma, such as just after penetrative sex, for example.

Having a miscarriage does not necessarily mean unsuccessful pregnancies in the future. Other symptoms that may accompany bleeding in miscarriages include severe lower abdominal pain, vaginal discharge of fluid or tissue and the disappearance of pregnancy symptoms such as nausea or breast tenderness.

Another cause of bleeding in early pregnancy is ectopic pregnancy. This occurs when the fertilised egg implants outside of the womb, for example in the Fallopian tubes. Generally the bleeding caused by an ectopic pregnancy would not be light and would be accompanied by severe abdominal pain often more to one side, with brown or watery vaginal discharge, shoulder tip pain (pain felt where your shoulder ends and your arm begins) and pain on urination or defecation. If you experience any of these symptoms, or heavy bleeding, then go to your doctor immediately.

Other pregnancy symptoms

Some women may not get any bleeding in early pregnancy but other symptoms will alert you to pregnancy, and if you have these alongside a light period it might help you tell (before doing a test) whether or not you are pregnant.

These symptoms can include morning sickness (which can actually occur at any time of the day). This symptom generally starts at around six weeks after the last period. Tiredness and mood swings are also common in the first 12 weeks of pregnancy due to the changes in hormone levels. You may find that your breasts enlarge, become very sensitive to touch, the nipples may darken or you may notice that the veins on the breast become particularly prominent.

Some women may find that they are needing to urinate more frequently and their bowel motions are slowed, and that they become more constipated. There may be increased vaginal discharge due to increased mucus production by the cervix. Some women may find their sense of smell and taste change, so that they have cravings for some foods and find other smells and foods off-putting.

Other causes of light periods

Aside from pregnancy, there are a lot of other conditions or factors which can cause light periods. For example, stress and anxiety can cause your periods to be irregular, light, or you might even miss one altogether. Once the stressful event has passed the periods should return to normal. Other symptoms that indicate stress or anxiety that might occur at the same time as your light period include palpitations, breathlessness, sweating, or tremors.

Women with an over- or under-active thyroid can also have irregular periods, as thyroid hormones form an integral part of the chain reaction that causes your menstrual cycle. Other symptoms you may notice include weight changes, general lethargy or hyper-activity and appetite changes. If you suspect your light period may be related to thyroid issues go and seek advice from your GP.

Taking contraceptive pills or having hormonal intra-uterine devices can lead to light periods, especially when you first start using a new type of contraception, as the body is still getting used to the hormones. Normally, after the body has adjusted, the irregular bleeding may stop.

Taking contraceptive pills or having hormonal intra-uterine devices can lead to light periods, especially when you first start using a new type of contraception.

Women with eating disorders such as anorexia and bulimia, who have low weight, can have periods which are very light, or their periods may stop altogether. This is because the release of hormones regulating periods are affected by extreme weight loss. If you have a very low body weight and your periods stop, or you are having trouble eating, go to your doctor as these conditions can lead to complications with your bone health and your reproductive health.

Women with polycystic ovary syndrome (PCOS) can also have light, and/or irregular periods. This is because the condition means you have a high level of androgens and excess insulin, which disrupts the ovulation cycle and therefore menstruation. Signs and symptoms of PCOS generally present in your teens or twenties, with irregular periods, difficulty getting pregnant, excessive hair growth, weight gain and oily skin.

When to see a doctor

If your periods suddenly become lighter and you think you may be pregnant, the only way to be sure is to take a pregnancy test. If the light bleeding is due to implantation, taking the test from 2-3 days after the start of the bleeding may show a positive result depending on the sensitivity of the urine test and the amount of hormones present in the body. But if the test is negative, it may still be too early, so wait another week and test again. Every woman is different and while for some the pregnancy test may be positive on the first day of your missed period, for others it may not be positive until up to one month after.

If you are not pregnant, having a noticeably light period from time to time normally isn’t the sign of any problem. Sometimes this may be due to temporary dysregulation in the menstrual cycle, such as during periods of stress. However, you should see a doctor if you have persistent irregular periods (where there is a lasting change in the pattern of menstruation), severe lower abdominal pain, or any other unusual symptoms such as excessive hair growth or weight loss, because these could be indicative of an underlying condition.

Dr. Diana Chiu MBChB (Hons), MRCP, PGCERT (Med Ed), PhD

Diana received her medical degree, with honours, from the University of Manchester. She then went on to receive basic and specialist medical training within the north west of England. She carried out in-depth research in medicine and was awarded a PhD in 2016. Currently, she is finishing her medical training at a large teaching hospital, and one of her greatest interests is medical education. She is an advanced life support instructor and writes regularly for post-graduate examination websites, and also holds a PGCERT in medical education with distinction.